The use of photovoltaic systems to generate power is increasingly establishing itself around the globe. Photovoltaic systems, also known as solar panel systems, can be easy to install, inexpensive to operate and can be used practically anywhere where sunlight is available. The various possibilities range from small fixed systems for home use right through to large solar parks with mobile solar modules that follow the position of the sun.
A photovoltaic source, such as a photovoltaic module including several photovoltaic cells, or a plurality of photovoltaic modules, should have optimal operation unaffected by irradiation from the sun, and the output voltage should be dependent directly on the degree of the instantaneous irradiation. Thus, when a cloud is shading the photovoltaic source the output voltage of the photovoltaic system can decrease. The direct correlation between the instantaneous irradiation and the output voltage can be a major issue in locations having a varying degree of irradiation.
The power mains, to which a photovoltaic source is arranged to feed electricity, specifies alternating current at a predetermined voltage level. In order to meet these specifications a DC/AC converter can be arranged between the photovoltaic source and the power mains, which converter can be arranged to operate at as wide an input voltage range as possible in order to manage a varying output voltage from the photovoltaic source. A converter managing a wide input voltage range can be proportionately expensive as it usually is comprised of more than one stage. A conventional way of managing a greatly varying input voltage is to use a boost DC/DC converter to provide a reasonable input voltage to said DC/AC converter. The use of a boost DC/DC converter at this stage can reduce the efficiency of the photovoltaic system.
DE 2646715 describes two generators, where a first is a photoelectric cell and the second can be a thermo-electric element. In one example, the two generators are connected in parallel with each other for loading a battery used for powering a load like a watch. One of the generators is disconnected from the other if it is not delivering enough power. This means that if one generator cannot deliver enough power, it gets disconnected or bypassed. If the remaining generator cannot deliver enough power, then the two generators are connected in series with each other. Finally, both generators are disconnected if the power from the two generators when connected in series is not enough.
FR 2335081 describes a device for enabling an accumulator to be recharged from a source of electrical energy, such as photo-cells. The device includes a converter circuit and a diode. The converter circuit can adapt the current and voltage supplied by said source to the charging conditions of the accumulator. The converter circuit is arranged to be saturated from a certain value of the current delivered by the source, the stronger currents passing directly through the diode.
WO 2006/041296 describes an apparatus for charging a battery, where a series connection of photovoltaic cells with a second battery is made in order to charge a first battery.
US 2002/146617 describes a solar cell that supplies power to a load. There is also a battery which supplies power to the load instead of the solar cell, when this is unable to. The battery includes a number of battery packs that can be selectively bypassed for reconditioning while the other remain on-line.
US 2003/230334 describes a cell that charges a battery via a converter. The battery also supplies power to a load via the converter.
EP 1901414 describes a solar cell used to load a battery for supplying power to a load in the form of a lamp. A converter is connected between solar cell and battery when loading.